Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$14.52	10.855%	$16.0961	$16.10	$16.10	$16.10
Purchase #2	$134.95	9.113%	$147.248	$147.25	$147.25	$147.20
Purchase #3	$88.96	11.572%	$99.2545	$99.25	$99.25	$99.30
Purchase #4	$169.70	3.528%	$175.687	$175.69	$175.70	$175.70
Purchase #5	$138.43	4.110%	$144.1195	$144.12	$144.10	$144.10
Purchase #6	$185.94	10.385%	$205.2499	$205.25	$205.25	$205.20
Purchase #7	$66.82	8.490%	$72.493	$72.49	$72.50	$72.50
7 purchase totals =	$799.32		$860.1480	$860.15	$860.15	$860.10